Hi just two more questions on the Headset ,

When should you know it needs to be replaced outright and when should it be a case of just changing the bearings ?The headset I have is very grainy to steer despite being well greased ,it doesnt adjust very well and there seems to be some wear on the crown race .Im sure its all put together properly and the bearings are in correctly .

What are common headset bearing sizes? . I bought some 5/32 inch bearings in races and they were much bigger than the ones in my headset .I dont have a callipers unfortunately to measure but are there many common sizes down from this?The bearings are in cages that are themselves in containers that can be pried open to put in grease ,the containers then sit in the cups of the headset .The headset is a classic External cup threadless headset .

Thanks for any help

First of all they're balls. Bearing refers to the entire assembly of races and balls.

Headsets rarely wear out in the classic sense since there's so little movement. They generally become "indexed" with clicked catches straight ahead and at intervals to either side. But the basic guideline is to replace when there's enough wear of any kind to be an issue.

Despite your claim otherwise I suspect you have a retainer upside down and the graininess you're feeling is because of that. This would especially apply if it wasn't as grainy before you serviced it. It's also possible that you're replacement retainer isn't correct for that headset.

Most experienced mechanics don't buy replacement retainers, and instead buy replacement balls and run our bearings (all) with loose balls.

Yes to everything FB said, and balls are cheap. You can buy a bag of 100 at the LBS and practice overhauli g the old headset. If it works, great. If not, change out the whole thing for new. You will still have plenty of balls left for several future overhauls. You can take an old ball to the LBS to get it measured or nust matched up with new ones.

The OP brings up a design aspect that I shake my head over. His small balls... in his headset. It's been my understanding for a few decades that the load capacity of a ball bearing increases geometrically to it's diameter but only linearly with the number of balls. So this headset with less then 5/32" balls likely uses 1/8" ones. This is about as tiny as one sees in the bike bearing world (excepting some thrust situations). This tiny a ball will pit, wear, and roll rough sooner then larger ones. It will tend to dent the cone or cup sooner (debate about denting VS fretting aside). It's only advantage is to allow a lower stack height or tighter fits between the head tube's ID and the steerer's OD. (Yet the common applications of 1/8" balled headsets that I've serviced don't seem to take advantage of these possible benefits). I've seen a lot of 1/8" balled headsets still roll rough with new proper sized balls (both w/ and w/out the retainer retained). I also feel that the small balls make for a touchier adjustment. Andy.

I've never seen balls smaller than 5/32" used in a headset (but I haven't seen every headset). The OP is offering too much info, some of which is contradictory. I'm starting to wonder if the headset had some kind of angular contact cartridge bearings, which he's taken apart -- the "containers" he's taken apart.

At this point, I'd want to see photos of the various parts before i could help him.

As for what's the best option in therms of ball size, it's hard to tell. Headsets are fairly lightly loaded, and are stationary bearings which die from fretting not wear. I don't know how significant ball size is in fretting failure. Most people consider fretting a lubrication, not mechanical failure.

I tend to clump a few forces at work under the "wear" heading. Adjustment condition, lube condition, fretting and or denting, rust, actual bearing wear, pitting. To the lay person there's not much difference as all leads to replacement. I am happy to talk about each factor separate of the others but I wonder how much is lost on the masses.

An example is what I suspect the OP has as a headset. There are some found on mid priced Treks and Giants (and likely many more brands) that have what could be called a cartridge design. Except that the cup surface is the cup, line a traditional loose ball design. The cone is held into this cup with a sloppy fitting plastic ring (sure, call it a seal, but not what some will think of as a seal on an industrial cartridge bearing). The balls are 1/8" and contained in a plastic holding ring. There is a conical centering ring on the fork crown and on the steerer (with a compression slot). Because of the plastic ball holder the open space within the bearing assembly is small. Because of the loose fitted "seal" the outside gets in easily (driving in the rain w/ bike on a rack). Because of the tiny balls any grit, rust, pitting, fretting or denting that happens feels greater then with a larger ball diameter. Because these headsets are found on the buy it and forget it bikes all this happens often enough for me to get disappointed often. I will do an overhaul, replacing the balls held in ring with loose, steel wool off the cup and cones for $10 or $15 during the tune up a number of times every year. I get far better then before results yet still feel the headset is really needing replacement. So I note the situation on the service ticket and move on. Rarely do I have a follow up talk with the customer and explain, when I do the differences between rust and fretting (to mention two forces) is lost. They see only a wear out part that they will live with more often then not. Andy.